Recently, display technologies using various methods such as a plasma display panel (PDP), a liquid crystal display (LCD) and the like that are used instead of a known brown tube in accordance with the development of optical technologies are suggested and sold. The higher properties of the polymer material for displays are required. For example, in the case of the liquid crystal display, according to the development toward the thin film, the lightness, and enlargement of the picture area, the wide viewing angle, the high contrast, the suppression of change in picture color tone according to the viewing angle and the uniformity of the picture display are particularly considered as important problems. Therefore, various polymer films such as a polarizing film, a retardation film, a plastic substrate, a light guide plate and the like are used, and in particular, in order to provide the retardation film for the wide viewing angle, a film in which a retardation function is provided by stretching various kinds of polymers has been suggested. These retardation films that have a single layer structure and a multilayered structure have been suggested.
For example, a method using a cyclic polyolefin polymer (COP) has been suggested (Japanese Patent Application Laid-Open Nos. 2001-350017 and 2004-51928). However, there is a problem in that the cyclic polyolefin resin has a reduced adhesion property in respects to other substrates such as films, and there is a problem in that since it has a small change ratio in retardation because of the extension, a sufficient retardation as a retardation film is not ensured.
Accordingly, in Japanese Patent No. 2886893, a copolymer resin of styrene and maleic anhydride that includes methyl methacrylate (MMA) as a main component and is extended is used as a retardation plate. As described in the patent document, if an acrylic resin is used, a retardation plate that is transparent, has no haze, and has a predetermined retardation obtained through the extension may be manufactured.
However, in the case of when the retardation film is manufactured as suggested in the patent document, because of the characteristics of an acrylic resin composition, the film is made brittle. Thus, there are problems in that unstability occurs in a roll while the film is processed and a difficulty in attachment to a polarizer occurs, which makes a processing process difficult, thus it is difficult for it to be used as the retardation film.
In addition, a multi-layered retardation film that is obtained by layering the acrylic film has been suggested by Japanese Patent Application Laid-Open No. 2006-192637. In the patent document, a styrene resin is used as an intermediate layer and an acrylic resin is layered on both sides for use.
However, as suggested in the patent document, if a styrene-maleic anhydride copolymerization resin is used in an intermediate layer and an acrylic resin that includes an acrylic rubber is used on both sides thereof, because of a difference between glass transition temperatures (Tg) of two layers, there is a problem in terms of heat resistance.